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                <h1 id="Java线程池简单了解"><a href="#Java线程池简单了解" class="headerlink" title="Java线程池简单了解"></a>Java线程池简单了解</h1><p>[TOC]</p>
<blockquote>
<p>主要查看文章：</p>
<p><a target="_blank" rel="noopener" href="https://mp.weixin.qq.com/s/baYuX8aCwQ9PP6k7TDl2Ww">Java线程池实现原理及其在美团业务中的实践 </a></p>
<p><a target="_blank" rel="noopener" href="https://snailclimb.gitee.io/javaguide/#/./docs/java/multi-thread/%E6%8B%BF%E6%9D%A5%E5%8D%B3%E7%94%A8%E7%9A%84%E7%BA%BF%E7%A8%8B%E6%B1%A0%E6%9C%80%E4%BD%B3%E5%AE%9E%E8%B7%B5">JavaGuide -线程池最佳实践</a></p>
<p><a target="_blank" rel="noopener" href="https://mp.weixin.qq.com/s?__biz=Mzg2OTA0Njk0OA==&mid=2247485808&idx=1&sn=1013253533d73450cef673aee13267ab&chksm=cea246bbf9d5cfad1c21316340a0ef1609a7457fea4113a1f8d69e8c91e7d9cd6285f5ee1490&token=510053261&lang=zh_CN&scene=21#wechat_redirect">新手也能看懂的线程池学习总结</a></p>
</blockquote>
<h2 id="1-为什么要用线程池"><a href="#1-为什么要用线程池" class="headerlink" title="1.为什么要用线程池"></a>1.为什么要用线程池</h2><p>池化思想，比如线程池，数据库连接池，HTTP连接池等。主要是为了能够重复利用资源，提高资源的利用率。</p>
<p>线程池的好处:</p>
<ul>
<li>降低资源消耗：可重复利用资源</li>
<li>提高响应速度：任务到达时，无需等待线程创建即可立即执行</li>
<li>提高线程可管理性：防止线程创建过多消耗尽系统资源内存等</li>
</ul>
<p><strong>线程池解决的核心问题：资源管理问题</strong></p>
<h2 id="2-Java线程池使用例子"><a href="#2-Java线程池使用例子" class="headerlink" title="2 Java线程池使用例子"></a>2 Java线程池使用例子</h2><h3 id="2-1-总览"><a href="#2-1-总览" class="headerlink" title="2.1 总览"></a>2.1 总览</h3><p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210527114738269.png" alt="Executor使用示意图"></p>
<ol>
<li><p>主线程首先创建实现 <code>Runnable</code> 或者 <code>Callable</code> 接口的<strong>任务对象</strong></p>
</li>
<li><p><strong>把创建完成的实现 <code>Runnable</code>/<code>Callable</code>接口的对象，直接交给 <code>ExecutorService</code> 执行</strong>: </p>
<ul>
<li><code>ExecutorService.execute（Runnable command）</code></li>
<li><code>ExecutorService.submit（Runnable task）</code></li>
<li><code>ExecutorService.submit（Callable &lt;T&gt; task）</code></li>
</ul>
<p>关于 <code>submit()</code> 与 <code>execute()</code> 区别看下面。</p>
</li>
<li><p>如果使用的submit提交，则会返回Future对象，包含执行结果。</p>
<p><code>FutureTask = Future + Runnable</code>，可以用它来直接提交任务与获得返回结果。</p>
</li>
<li><p>主线程<code>future.get()</code>获取返回结果，或者主线程 <code>FutureTask.cancel（boolean mayInterruptIfRunning）</code>来取消此任务的执行，参数boolean表示是否让任务完成。</p>
</li>
</ol>
<h4 id="submit与execute"><a href="#submit与execute" class="headerlink" title="submit与execute"></a>submit与execute</h4><ol>
<li><p><code>execute()</code>方法用于提交<strong>不需要返回值的任务</strong>，所以<strong>无法判断</strong>任务是否被线程池执行<strong>成功与否</strong>；</p>
</li>
<li><p><code>submit()</code>方法用于提交<strong>需要返回值的任务</strong>。</p>
<p>线程池会返回一个 <strong><code>Future</code> 类型的对象</strong>，通过这个 <code>Future</code> 对象可以判断任务是否执行成功</p>
<ul>
<li><p>可以通过 <code>Future</code> 的 <code>get()</code>方法来<strong>获取返回值</strong>，<code>get()</code>方法会<strong>阻塞当前线程直到任务完成</strong>；</p>
</li>
<li><p>而使用 <code>get（long timeout，TimeUnit unit）</code>方法则会<strong>阻塞当前线程一段时间后立即返回</strong>，这时候有可能任务没有执行完。</p>
</li>
</ul>
</li>
</ol>
<h3 id="2-2-ThreadPoolExecutor实例"><a href="#2-2-ThreadPoolExecutor实例" class="headerlink" title="2.2 ThreadPoolExecutor实例"></a>2.2 ThreadPoolExecutor实例</h3><p>==<strong>Java中的线程池：ThreadPoolExecutor</strong>==</p>
<p>ThreadPoolExecutor的构造函数，用它来创建线程池：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token comment">/**
 * 用给定的初始参数创建一个新的ThreadPoolExecutor。
 */</span>
<span class="token keyword">public</span> <span class="token class-name">ThreadPoolExecutor</span><span class="token punctuation">(</span><span class="token keyword">int</span> corePoolSize<span class="token punctuation">,</span><span class="token comment">//线程池的核心线程数量</span>
                          <span class="token keyword">int</span> maximumPoolSize<span class="token punctuation">,</span><span class="token comment">//线程池的最大线程数</span>
                          <span class="token keyword">long</span> keepAliveTime<span class="token punctuation">,</span><span class="token comment">//当线程数大于核心线程数时，多余的空闲线程存活的最长时间</span>
                          <span class="token class-name">TimeUnit</span> unit<span class="token punctuation">,</span><span class="token comment">//时间单位</span>
                          <span class="token class-name">BlockingQueue</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Runnable</span><span class="token punctuation">></span></span> workQueue<span class="token punctuation">,</span><span class="token comment">//任务队列，用来储存等待执行任务的队列</span>
                          <span class="token class-name">ThreadFactory</span> threadFactory<span class="token punctuation">,</span><span class="token comment">//线程工厂，用来创建线程，一般默认即可</span>
                          <span class="token class-name">RejectedExecutionHandler</span> handler<span class="token comment">//拒绝策略，当提交的任务过多而不能及时处理时，我们可以定制策略来处理任务</span>
                           <span class="token punctuation">)</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<p>这几个参数，稍微记一下：</p>
<ul>
<li>核心线程数量</li>
<li>最大线程数量</li>
<li>存活时间（当前线程数 &gt; 核心线程数，多余线程的最长存活时间）</li>
<li>时间单位（TimeUnit.SECONDS）</li>
<li>任务队列</li>
<li>线程工厂，一般默认不用管</li>
<li>拒绝策略（任务过多时，定制策略处理任务）</li>
</ul>
<p>创建例子：</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token comment">/** 核心线程数 **/</span>
<span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> CORE_POOL_SIZE <span class="token operator">=</span> <span class="token number">5</span><span class="token punctuation">;</span>
<span class="token comment">/** 最大线程数 **/</span>
<span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> MAX_POOL_SIZE <span class="token operator">=</span> <span class="token number">10</span><span class="token punctuation">;</span>
<span class="token comment">/** 队列容量 **/</span>
<span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token keyword">int</span> QUEUE_CAPACITY <span class="token operator">=</span> <span class="token number">100</span><span class="token punctuation">;</span>
<span class="token comment">/** 最大存活时间 **/</span>
<span class="token keyword">private</span> <span class="token keyword">static</span> <span class="token keyword">final</span> <span class="token class-name">Long</span> KEEP_ALIVE_TIME <span class="token operator">=</span> <span class="token number">1L</span><span class="token punctuation">;</span>

<span class="token keyword">public</span> <span class="token keyword">static</span> <span class="token keyword">void</span> <span class="token function">main</span><span class="token punctuation">(</span><span class="token class-name">String</span><span class="token punctuation">[</span><span class="token punctuation">]</span> args<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>

    <span class="token comment">//使用阿里巴巴推荐的创建线程池的方式</span>
    <span class="token comment">//通过ThreadPoolExecutor构造函数，自定义参数创建</span>
    <span class="token class-name">ThreadPoolExecutor</span> executor <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ThreadPoolExecutor</span><span class="token punctuation">(</span>
            CORE_POOL_SIZE<span class="token punctuation">,</span>
            MAX_POOL_SIZE<span class="token punctuation">,</span>
            KEEP_ALIVE_TIME<span class="token punctuation">,</span>
            <span class="token class-name">TimeUnit</span><span class="token punctuation">.</span>SECONDS<span class="token punctuation">,</span>
            <span class="token keyword">new</span> <span class="token class-name">ArrayBlockingQueue</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token punctuation">></span></span><span class="token punctuation">(</span>QUEUE_CAPACITY<span class="token punctuation">)</span><span class="token punctuation">,</span>
            <span class="token keyword">new</span> <span class="token class-name">ThreadPoolExecutor<span class="token punctuation">.</span>CallerRunsPolicy</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

    <span class="token comment">// 循环，线程池中，创建10个线程</span>
    <span class="token keyword">for</span> <span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">&lt;</span> <span class="token number">10</span><span class="token punctuation">;</span> i<span class="token operator">++</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        <span class="token comment">// Lambda表达式，调用execute的参数类型Runnable接口的构造函数，返回匿名对象并实现其中方法（大括号中）</span>
        <span class="token comment">// 相当于new Runnable()&#123; run()&#123;&#125; &#125;</span>
        executor<span class="token punctuation">.</span><span class="token function">execute</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-></span> <span class="token punctuation">&#123;</span>
            <span class="token keyword">try</span> <span class="token punctuation">&#123;</span>
                <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">sleep</span><span class="token punctuation">(</span><span class="token number">2000</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token punctuation">&#125;</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> e<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
                e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
            <span class="token punctuation">&#125;</span>
            <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"CurrentThread name:"</span> <span class="token operator">+</span> <span class="token class-name">Thread</span><span class="token punctuation">.</span><span class="token function">currentThread</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">.</span><span class="token function">getName</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">+</span> <span class="token string">"；date："</span> <span class="token operator">+</span> <span class="token class-name">Instant</span><span class="token punctuation">.</span><span class="token function">now</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
        <span class="token punctuation">&#125;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
    <span class="token comment">//终止线程池</span>
    executor<span class="token punctuation">.</span><span class="token function">shutdown</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">try</span> <span class="token punctuation">&#123;</span>
        <span class="token comment">// 等待所有任务完成</span>
        executor<span class="token punctuation">.</span><span class="token function">awaitTermination</span><span class="token punctuation">(</span><span class="token number">5</span><span class="token punctuation">,</span> <span class="token class-name">TimeUnit</span><span class="token punctuation">.</span>SECONDS<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span> <span class="token keyword">catch</span> <span class="token punctuation">(</span><span class="token class-name">InterruptedException</span> e<span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
        e<span class="token punctuation">.</span><span class="token function">printStackTrace</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token punctuation">&#125;</span>
    <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"Finished all threads"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
<span class="token punctuation">&#125;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>

<ol>
<li><code>ThreadPoolExecutor</code>构造函数创建线程池</li>
<li>线程池中运行线程 <code>executor.execute(Runnable r)</code></li>
<li>终止线程池 <code>exector.shutdown()</code></li>
</ol>
<blockquote>
<p>其中，关于Lamda表达式-&gt;：Lambda 允许把函数作为一个方法的参数（函数作为参数传递进方法中）。</p>
<p>下面这个例子就是调用了一个<strong>构造函数</strong>，返回了一个新建的对象，然后传入<strong>函数参数</strong>中。</p>
<pre class="line-numbers language-java" data-language="java"><code class="language-java"><span class="token class-name">EventQueue</span><span class="token punctuation">.</span><span class="token function">invokeLater</span><span class="token punctuation">(</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token operator">-></span> <span class="token punctuation">&#123;</span>
      <span class="token class-name">JFrame</span> frame <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ImageViewerFrame</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      frame<span class="token punctuation">.</span><span class="token function">setTitle</span><span class="token punctuation">(</span><span class="token string">"ImageViewer"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      frame<span class="token punctuation">.</span><span class="token function">setDefaultCloseOperation</span><span class="token punctuation">(</span><span class="token class-name">JFrame</span><span class="token punctuation">.</span>EXIT_ON_CLOSE<span class="token punctuation">)</span><span class="token punctuation">;</span>
      frame<span class="token punctuation">.</span><span class="token function">setVisible</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
  <span class="token punctuation">&#125;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>

<span class="token class-name">EventQueue</span><span class="token punctuation">.</span><span class="token function">invokeLater</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">Runnable</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
      <span class="token keyword">public</span> <span class="token keyword">void</span> <span class="token function">run</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">&#123;</span>
          <span class="token class-name">JFrame</span> frame <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">ImageViewerFrame</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
          frame<span class="token punctuation">.</span><span class="token function">setTitle</span><span class="token punctuation">(</span><span class="token string">"ImageViewer"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
          frame<span class="token punctuation">.</span><span class="token function">setDefaultCloseOperation</span><span class="token punctuation">(</span><span class="token class-name">JFrame</span><span class="token punctuation">.</span>EXIT_ON_CLOSE<span class="token punctuation">)</span><span class="token punctuation">;</span>
          frame<span class="token punctuation">.</span><span class="token function">setVisible</span><span class="token punctuation">(</span><span class="token boolean">true</span><span class="token punctuation">)</span><span class="token punctuation">;</span>
      <span class="token punctuation">&#125;</span>
  <span class="token punctuation">&#125;</span><span class="token punctuation">)</span><span class="token punctuation">;</span><span aria-hidden="true" class="line-numbers-rows"><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span><span></span></span></code></pre>
</blockquote>
<h2 id="3-线程池核心设计与实现总览"><a href="#3-线程池核心设计与实现总览" class="headerlink" title="3.线程池核心设计与实现总览"></a>3.线程池核心设计与实现总览</h2><p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526110139152.png" alt="ThreadPoolExecutor的UML类图"></p>
<p>这个UML看的不是很懂。。。继续往下看</p>
<p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526110421744.png" alt="ThreadPoolExecutor运行流程"></p>
<h2 id="4-线程池生命周期"><a href="#4-线程池生命周期" class="headerlink" title="4. 线程池生命周期"></a>4. 线程池生命周期</h2><p>其中，线程池 <code>ThreadPoolExecutor</code>的状态有5种：</p>
<p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526224430777.png" alt="ThreadPoolExecutor状态5种"></p>
<p>其状态转移图：</p>
<p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526224536641.png" alt="5种状态的转移"></p>
<h2 id="5-任务执行机制"><a href="#5-任务执行机制" class="headerlink" title="5. 任务执行机制"></a>5. 任务执行机制</h2><p>线程池的本质是对<strong>任务和线程</strong>的管理，而做到这一点==最关键的思想就是将任务和线程两者解耦==，不让两者直接关联，才可以做后续的分配工作。</p>
<p>线程池中是以<strong>生产者消费者模式</strong>，通过一个阻塞队列来实现的。</p>
<p>阻塞队列缓存任务，工作线程（消费者）从阻塞队列中获取任务。</p>
<p>分为以下几个模块：</p>
<ul>
<li>任务调度</li>
<li>任务缓冲</li>
<li>任务申请</li>
<li>任务拒绝</li>
</ul>
<h3 id="5-1-任务调度"><a href="#5-1-任务调度" class="headerlink" title="5.1 任务调度"></a><strong>5.1 任务调度</strong></h3><p>一个任务提交到线程池了之后，会经过一下判断</p>
<p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526225421822.png" alt="image-20210526225421822"></p>
<h3 id="5-2-任务缓冲"><a href="#5-2-任务缓冲" class="headerlink" title="5.2 任务缓冲"></a><strong>5.2 任务缓冲</strong></h3><p>任务缓冲模块是线程池能够管理任务的<strong>核心部分</strong>。</p>
<p>线程池的本质是对<strong>任务和线程</strong>的管理，而做到这一点==最关键的思想就是将任务和线程两者解耦==，不让两者直接关联，才可以做后续的分配工作。</p>
<p>线程池中是以<strong>生产者消费者模式</strong>，通过一个阻塞队列来实现的。</p>
<p>阻塞队列缓存任务，工作线程（消费者）从阻塞队列中获取任务。</p>
<p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526232913936.png" alt="阻塞队列示意"></p>
<blockquote>
<p>阻塞队列(BlockingQueue)是一个支持两个附加操作的队列。</p>
<p>这两个附加的操作是：</p>
<ul>
<li>在队列为空时，获取元素的线程会等待队列变为非空。</li>
<li>当队列满时，存储元素的线程会等待队列可用。</li>
</ul>
<p>阻塞队列常用于生产者和消费者的场景：</p>
<ul>
<li>生产者是往队列里添加元素的线程</li>
<li>消费者是从队列里拿元素的线程</li>
</ul>
<p>阻塞队列就是生产者存放元素的<strong>容器</strong>，而消费者也只从容器里拿元素。</p>
<p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526230357982.png" alt="阻塞队列成员"></p>
</blockquote>
<h3 id="5-3-任务申请"><a href="#5-3-任务申请" class="headerlink" title="5.3 任务申请"></a>5.3 任务申请</h3><p>任务的执行有两种可能：</p>
<ul>
<li>一种是<strong>任务直接由新创建的线程执行</strong>（仅出现在线程初始创建的时候）</li>
<li>另一种是线程从<strong>任务队列中获取任务</strong>然后执行，执行完任务的空闲线程会再次去从队列中申请任务再去执行（线程获取任务绝大多数的情况）</li>
</ul>
<p>线程池中的<strong>线程</strong>去<strong>申请任务</strong>的步骤：</p>
<p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526231424192.png" alt="线程申请任务步骤"></p>
<p>申请任务时，通过一个 <code>getTask()</code>去执行，经过以上判断的<strong>目的是为了防止线程池中的线程过多，控制线程数量</strong>。</p>
<h3 id="5-4-任务拒绝"><a href="#5-4-任务拒绝" class="headerlink" title="5.4 任务拒绝"></a>5.4 任务拒绝</h3><p>任务拒绝模块是线程池的==保护部分==。</p>
<p>线程池有一个<strong>最大的容量</strong>，当线程池的<strong>任务缓存队列已满</strong>，并且线程池中的<strong>线程数目达到maximumPoolSize</strong>时，就需要拒绝掉该任务，采取任务拒绝策略，保护线程池。</p>
<p><code>RejectedExecutionHandler</code> 是一个<strong>接口</strong>，可以自定义拒绝策略。</p>
<p>也可以用JDK自带的4种拒绝策略：</p>
<p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210526232150795.png" alt="JDK自带的4种拒绝策略"></p>
<h2 id="6-使用场景举例"><a href="#6-使用场景举例" class="headerlink" title="6.使用场景举例"></a>6.使用场景举例</h2><h3 id="场景1：快速响应用户请求"><a href="#场景1：快速响应用户请求" class="headerlink" title="场景1：快速响应用户请求"></a><strong>场景1：快速响应用户请求</strong></h3><p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210527112123842.png" alt="并行执行任务提升任务响应速度"></p>
<blockquote>
<p><strong>描述</strong>：用户发起的实时请求，服务追求响应时间。比如说用户要查看一个商品的信息，那么我们需要将商品维度的一系列信息如商品的价格、优惠、库存、图片等等聚合起来，展示给用户。</p>
</blockquote>
<p>这种场景最重要的就是获取最大的响应速度去满足用户，</p>
<p>所以应该<strong>不设置队列去缓冲并发任务</strong>，<strong>调高corePoolSize和maxPoolSize</strong>去<strong>尽可能创造多的线程</strong>快速执行任务。</p>
<h3 id="场景2：快速处理批量任务"><a href="#场景2：快速处理批量任务" class="headerlink" title="场景2：快速处理批量任务"></a><strong>场景2：快速处理批量任务</strong></h3><p><img src="https://gitee.com/songx86/SongPicBed/raw/master/img/image-20210527112403454.png" alt="并行执行任务提升批量任务执行速度"></p>
<blockquote>
<p><strong>描述</strong>：离线的大量计算任务，需要快速执行。比如说，统计某个报表，需要计算出全国各个门店中有哪些商品有某种属性，用于后续营销策略的分析，那么我们需要查询全国所有门店中的所有商品，并且记录具有某属性的商品，然后快速生成报表。</p>
</blockquote>
<p>这类场景任务量巨大，并不需要瞬时的完成，而是关注如何使用有限的资源，尽可能在单位时间内处理更多的任务，也就是吞吐量优先的问题。</p>
<p>设置<strong>队列去缓冲并发任务</strong>，调整合适的corePoolSize去设置处理任务的线程数</p>
<p>设置的<strong>线程数过多</strong>可能还会引发线程上下文切换频繁的问题，也会降低处理任务的速度，降低吞吐量。</p>
<h2 id="7-几个对比"><a href="#7-几个对比" class="headerlink" title="7. 几个对比"></a>7. 几个对比</h2><ul>
<li>Runnable 与 Callable：前者不抛异常/返回结果，后者会</li>
<li>execute() 与 submit()：前者不会返回结果，后者会</li>
<li>shutdown() 与 shutdownNow()：前者会等待队列中的任务执行完毕，后者不会</li>
<li>isShutdown() 与 isTeminated() ：前者是shutdown()了之后就true，后者是等全部执行完成了之后才true</li>
</ul>
<h2 id="总结"><a href="#总结" class="headerlink" title="总结"></a>总结</h2><p>如何回答线程池原理：</p>
<p>感觉只要答出，任务–线程解耦，以及阻塞队列，生产者消费者模式，就可以了，这几个是重点。</p>

                
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